The application of polymeric materials to body tissues of human or animal patients is becoming increasingly important in medicine. Among the proposed uses of such materials are the alteration of tissue; the creation or preservation of lumens, channels or reservoirs for the passage or collection of fluids; the creation of matrices for the growth of tissue; the control of undesirable tissue growth; the delivery of therapeutic agents to a tissue surface; the ability to join a tissue surface to another tissue or an artificial implant; the ability to isolate or protect tissue or lesions to enable or mediate healing; and the ability to mediate the rate of substances or energy passing into, out of, or through tissue.
Although it has been recognized that the use of polymeric materials in vivo may offer significant therapeutic effects, to date such applications have met many limitations. For example, the methods for applying such polymers to tissue surfaces often require the use of pressure, heat or electrical energy exceeding limits of tolerability at the tissue site. Likewise various chemical effects associated with such polymers have been found to be physiologically unacceptable.
Numerous methods for reshaping polymeric materials in vivo are known in the prior art. In particular, U.S. Pat. No. 5,213,580 and International Publication WO 90/01969, both to Slepian et al., the entire disclosures of which are incorporated herein by reference, describe methods in which polymers having melting points slightly above physiological temperatures are implanted into a patient and in which such polymers are melted via contact with heated fluids and shaped using mechanical force provided by a balloon catheter. Unfortunately, many of the methods known in the art suffer from the need to use energy levels beyond those which are physiologically tolerable, or from the inability to sufficiently control the shape change and/or temperature of the polymeric material.
Typically, the primary limitation in prior art methods for the delivery of energy to an implanted device is the inability to direct the energy specifically to the device, while minimizing energy delivery to body tissue. For example, it is known in the prior art that polymeric devices such as stents may be delivered to specific locations in vivo using a balloon catheter. Such stents may be heated at the site by filling the balloon with a heated fluid. In that method, heat is conducted from the fluid in the balloon, through the balloon material, and into the stent. Since conduction is a relatively slow process and the balloon has a relative large thermal mass, energy is transferred not only to the stent, but also to the surrounding body tissues and fluids. The result is that undesired amounts of heat are transferred into the surrounding body tissues and fluids.
Accordingly, a need exists for apparatus for implanting polymeric materials in vivo that avoids the problems associated with the prior art. A need also exists for methods for delivering and reshaping materials in vivo which allow a physician to safely and easily introduce the material into a patient, configure the material as desired, and deposit the material at a desired location for at least a therapeutically desirable period of time. A further need exists for materials and methods for reshaping such materials in vivo that offer the ability to reshape the materials while minimizing the amount of energy that is transferred to surrounding tissues and physiological fluids.